1. Field of the Invention
The present invention relates to an apparatus for connecting semiconductor devices, such as LSI chips, to a wiring board, wherein the semiconductor devices have highly dense electrodes for gate arrays and microcomputers.
2. Description of the Prior Art
To explain the background of the present invention, reference will be made to FIGS. 1a, 1b and 1c :
For connecting LSI chips to wiring boards many systems are known and used, such as wire bonding, flip chip bonding, film carrier bonding. FIG. 1a shows a typical example of the wire bonding system.
Under the wire bonding system wires of Au Al, etc. and conductors 75 are individually connected to the electrodes of Al of an LSI chip 71 and a wiring board 74, respectively, by use of bonding capillaries 76 permitting pressure or supersonic wave oscillation to be applied. FIG. 1b shows the flip chip bonding system, under which the conductor 75 of the wiring board 74 is provided with solder pedestals 79 and the LSI chips 71 are provided with bumps 78. By using a bonding tool 77, which permits heating, pressuring, and sucking of chips, the pedestals 79 and the bumps 78 are bonded to each other. Afterwards, the reflow of solder is effected. FIG. 1c shows a film carrier bonding system, under which the inner lead 82 of a film carrier 81 is bonded to the bumps of Au of the LSI chip 71 by heat and pressure.
Another bonding system is disclosed in U.S. Pat. No. 4,749,120. According to this prior art method an LSI chip is placed face down and fixed to a wiring board with insulating resin of a photo-setting nature. Referring to FIGS. 2a, 2b and 2c, it will be more particularly described. As shown in FIG. 2a, a wiring board placed on a wiring board setting stage 93 of metal is coated with insulating resin 90 of a photo-setting nature. The bump electrodes 76 of the LSI chip 96 are aligned with the conductors 91 and the chip 96 is mounted on the wiring board 92. Then a pressing tool 94 is placed in contact with the chip 96 under hydraulic pressure. In this way the chip 96 is pressed against the wiring board until it comes into contact with the wiring board, during which the resin therebetween is squeezed and spreads out. At this stage ultra violet rays 95 are injected so as to harden the resin. Then the pressure is released as shown in FIG. 2c, and the resin is allowed to harden to form a bed in which the bump electrodes and the conductors 91 are embedded together.
The conventional systems described above have the following disadvantages:
(1) The wire bonding system consumes time and labor, particularly when a number of pins are used, because of the necessity of connecting the wires individually. This reflects in the cost. In addition, the bonding capillary 58 must have a certain degree of strength, and because of this, the size cannot easily be reduced. The resulting minimum pitch is about 150 microns, which is not suitable for LSI chips.
(2) The flip chip system must heat the bonding tools 77, 80, and the heat is likely to damage the LSI chips, particularly the film carrier bonding system requiring a high temperature in the range of 300.degree. C. to 500.degree. C. As a result, the bonding tool 80 must be made of a material safe from deformation, elongation or contraction due to high temperatures heat. Such materials are expensive. As a whole the production cost is increased.
(3) The maximum connecting pitch of the flip chip system is 250 .mu.m, and that of the film carrier system is 100 .mu.m. These systems are not suitable for a highly dense connection.
(4) Each system requires extra equipment: for example, the wire bonding system requires a die bonder and a wire bonder, the film carrier system requires an inner lead bonder and an outer lead bonder, and the flip chip system requires a flip chip bonder and a reflow furnace. In this way each system requires at least two kinds of equipment, which reflect in the production cost.
The micro bump bonding system has the following disadvantages:
(1) Since the wiring board setting stage 93 is made of metal, it is difficult to secure a flat substrate surface. Owing to the uneven surface, the pressing force is unevenly applied to the bumps of the chip 96, thereby leading to defective connections.
(2) Since the LSI chip is pressed by a hydraulic cylinder, the applicable load is limited to a range of a to 5a, where the a is the value of the minimum applicable load. As a result, the applicability of this system is limited to a particular number of the electrodes of an LSI chip and its size. This system employs a cam for reducing an impact upon the LSI chip, but the use of a cam is disadvantageous in that it must be replaced so as to be in agreement with the thicknesses of the wiring board and the chip. The frequent replacement of cams retards the production. Since the pressing tool 94 is stationary and lacks flexibility, it is difficult to adapt to varying conditions; for example, when there is any disaccord between the LSI chip and the pressing tool because of unevenness present either in the wiring board or the wiring board setting stage or both. The pressing force is unevenly applied, thereby causing defective connections.